chpt 4 1

BIPOLAR JUNCTION BIPOLAR JUNCTION TRANSISTORS (BJTs)TRANSISTORS (BJTs)

have considered the junction diodehave considered the junction diode - basic - basic 2-terminal device2-terminal device

now consider the 3-terminal devicenow consider the 3-terminal device - much - much more usefulmore useful

3-terminal device: use voltage between 2 3-terminal device: use voltage between 2 terminals so as to control the current in terminals so as to control the current in the 3rd terminalthe 3rd terminal

chpt 4 2

3-terminal devices3-terminal devices

2 major types : 2 major types : - bipolar junction transistors (BJTs)- bipolar junction transistors (BJTs)

(chpt. 4)(chpt. 4) - field-effect - field-effect transistors (FETs)transistors (FETs) (chpt. 5)(chpt. 5)

chpt 4 3

Physical Structure of BJTPhysical Structure of BJT 3 semiconductor 3 semiconductor

regions:regions:- emitter (- emitter (nn))- base (- base (pp))- collector (- collector (nn))

= ‘= ‘npnnpn’ ’ transistortransistor

chpt 4 4

npnnpn - transistor modes - transistor modes

BJT modesBJT modes

MODE EBJ bias CBJ bias

CUTOFF Reverse Reverse

ACTIVE FORWARD Reverse

SAT. FORWARD FORWARD

chpt 4 5

npnnpn in ACTIVE MODE in ACTIVE MODE- current flow- current flow